Andrew Minshull, described as the 'main man' of the wheelclamping firm. Photograph: David Jones/PA

Five members of a car clamping operation that used motorists "as a licence to print money" have been jailed for a total of almost eight years.

Andrew Minshull, Debbie Worton, Simon Barry, Christopher Cartwright and Faisal Qadeer remained impassive in the dock at Worcester crown court as Judge John Cavell condemned them for "milking" the public out of up to £500,000.

Minshull, 38, who was described by the judge as the "main man" at the company, was jailed for 32 months, while his ex-partner, Debbie Worton, 43 – the "public face of the company" – was sentenced to 12 months.

Barry, 38, who took part in clamping and also liaised with landowners, was given a 21-month jail term, while Cartwright, 31, and Qadeer, 35, who selected victims in their roles as frontline operatives, were each jailed for 15 months.

Minshull, Worton and Qadeer, of Redditch, Barry, of Evesham, and Cartwright, of Kidderminster, all pleaded guilty in January of conspiracy to defraud.

Describing the company's treatment of drivers between 2006 and 2009 as disgraceful, Cavell told the defendants: "It is of course something that most people accept that illegal parking can cause very real problems to traders and other people and there can be no reasonable objection to the control of illegal parking by legitimate and proper enforcement.

"What of course is wholly wrong is the use of enforcement measures not to provide a service to help traders and others suffering from illegally parked cars, but to use the company as a vehicle to obtain money dishonestly from the public by blatant abuse of authority and power.

"In my judgment that is plainly what happened in this case."

The conduct of the company's staff as they conned the public had, on occasion, been offensive and intimidating, causing an element of fear as well as distress, the judge added.

The court heard that the conspiracy may have netted up to £500,000, although Cavell accepted that, if the figure was accurate, some of it may have been legitimate income.

Opening the facts of the case, the prosecutor, Anthony Potter, outlined how Midland Parking Contracts used underhand tactics and intimidated drivers into parting with up to £335 to unclamp vehicles and "cancel" tow-trucks that had not been called out.

Money was even demanded before clamps had been applied and unlit signs were used at night.

Operating at a total of 19 sites, Minshull's firm was the subject of a long-running joint investigation involving West Mercia Constabulary and Worcestershire's trading standards department.

The inquiry, also backed by the Security Industry Authority, was prompted by hundreds of complaints from members of the public living across the West Midlands, Gloucestershire and Warwickshire.

Potter said the company's victims, which included meter readers for water and power companies, a disabled woman displaying a blue badge and an NHS worker transporting blood samples, were targeted in Redditch, Nuneaton, Evesham, Worcester, Coventry, Bromsgrove and Cheltenham between March 2006 and August 2009.

Warning signs were either not prominent, obscured by a company vehicle, or on at least one occasion were erected after motorists had parked.

The court also heard that Worton used an alias to fob off aggrieved drivers who complained by telephone, while appeal letters and county court judgments were ignored by the firm, which had a postal address in Birmingham.

A sixth defendant, the wheelclamper Lloyd Isherwood, 39, of Birmingham, has also admitted conspiracy to defraud and will be sentenced at a later date.